Not advertising but a recommendation based on how often I get that wretched message
An unknown error has occurred. Account: 'pop.xxx.co.uk', Server: 'smtp.xxx.co.uk', Protocol: SMTP, Server Response: '421 Cannot connect
etc etc.
Of my two accounts, my yahoo account is far the more unreliable, such messages appearing all too often on Outlook Express for forwarded mail.
On the other hand, my google account (I whisper this in case it hears) has never failed in this manner and is always connected to Outlook Express.
And needless to say, if you are going to use an ANDROID device, googlemail is the internet to use.